1. Field of the Invention
The present invention relates to bulk bags for the storage and transport of bulk materials, and to support devices for making such bulk bags.
2. Description of the Prior Art
Bags for storage and transport of bulk materials, for example half-tonne, one-tonne, or two-tonne capacity bags, are typically of generally cuboid shape, formed from a fabric material such as polypropylene. Typically, the weight of fabric material will be from about 180 g/m2 to 400 g/m2 depending on the intended load and operating conditions. The fabric may be reinforced for extra strength.
The bags have a top which is either permanently fully open or which can be opened, for loading. The bottoms of the bags are typically provided with a discharge spout through which the contents of the bag can be emptied when the spout is opened. Alternatively, the base of the bag may be cut to discharge the contents if the bag is not to be re-used.
To enable such bags to be lifted and manoeuvred by a fork-lift truck, each bag is typically provided with a lifting strap at each corner. Such bags are often called Flexible Intermediate Bulk Containers (FIBC), or bulk bags. The term “bulk bags” will be used herein to denote such bags.
To lift a filled bulk bag, a fork-lift operator brings the tines of the fork close to the top of one edge of the filled bag so that each tine is adjacent to a lifting strap. An assistant lifts up each lifting strap to enable a tine to pass through the strap while the operator moves the tines forward over the bag. The fork-lift operator moves the tines further over the top of the bag until the tines are adjacent the rear pair of lifting straps, and the process is repeated so that the tines are disposed through the rear lifting straps. The bulk bag can then be lifted and moved.
A problem with this procedure is that there is a danger of injury to the assistant when the tines or the fork are moved. This is a particular problem when filled bulk bags are stacked high, on top of each other. The fork-lift operator is unable to see the rear pair of lifting straps when the stack is too high, and the assistant may be injured by a tine or pushed off a ladder. It is also costly to employ two men to secure the bulk bag on the fork.
If no assistant is present, the fork-lift operator must move the truck so that the tines of the fork are positioned near the front straps. He must then get out of the cab of the truck, hook the front straps over the tines, and get back in the cab. He must then drive the truck forward as far as he thinks necessary, get out again, hook the rear straps onto the tines (if he has judged the forward distance correctly), get back in the cab, drive further forward to pick up the bulk bag. The procedure is slow and can be dangerous.
To facilitate lifting of a bulk bag, it has been proposed in EP 0 259 230 to provide a rigid tubular cruciform structure to be secured in the straps of a bag so that pairs of tubes can receive the tines of a fork. In FR 2 721 304 it has been proposed to provide a similar disposable structure made of cardboard. To reduce the load to which lifting straps are subjected it has been proposed to provide bags with integral lifting slings along opposite top edges so that the load is spread out along those edges; see for example GB 1 549 448, GB 2 050 298, GB 2 092 990, and WO 97/37908. However, the use of such slings does not remove the need for a fork-lift operator either to leave the cab of his truck or to use an assistant to hook the tines of the fork-lift in the slings.
In WO 99/35058 it has been proposed to provide a bulk bag with a pair of parallel tubular guide members along the tops of opposed edges of the bulk bag. The tubular members are resilient and connected together by rigid spacing means at or adjacent to their ends. The lifting straps are supported upright by the tubular members, which function as guides for the tines of a fork-lift. This enables a fork-lift operator to insert the tines of the fork-lift through all four lifting straps in one movement and without leaving his cab. The tubular members may be formed from rubber or reinforced with a helically-wound wire of metal or a plastics material so that they lie flat when under load but revert to a predetermined sectional shape when the load is removed. The resilience of the tubular members allows stacking of filled bulk bags without significant wasted space. Bulk bags with self-raising straps are also described in U.S. Pat. No. 4,300,608. A problem we have found with such devices is that, if a heavy load is applied for a long time, the strap straps or tubular members may not recover, or not fully recover, their initial shape so that insertion of a fork-lift's tines may be difficult or impossible without manual intervention.